Travelling wave tubes with crossed electric and magnetic fields



2,942,140 Rossn LDS om m DICH uwn BwwZ mwmm U Du GWNJ AnAd awc e GGIH.. F

June 21, 1960 TRAVELLIN ELECTR TRAVLLING WAVE TUBES WITH CROSSEI) ELECTRIC .AND MAGNETIC FIELDS 'GeorgesGuilbaum Paris, France, assigner to Compagnie `Generale de Telegraphie Sans Fil, a corporation of lFrance Travelling wave tubes with crossed electric Zand magnetic Afields generally comprise a. conductive delay line and "a vconductive negative electrode, generally known as av sole. 'The delay line and electrode bound what is called the interaction space, and the potential of the delay line is high with respect to that ofthe negative electrode. An Velectron beam is projected into the interaction space for propagation in a direction parallel to the delay line. A magnetic teld is provided in this space, perpendicu- "larly to the directions of the beam and of the electric field due to the potential diierence between the delay line andthe negative electrode.

As is Well known, in tubes of this type, and more particularly in high power tubes, some of the beam elec- 4trons `reach the negative electrode and give rise therein Ato an undesirable current which increases the nolse 1n the tube.

It is an object of the present invention to provide a tube of the above described type which does not present this disadvantage.

The tube, according 'to the invention, has an interaction space of .constant width and is provided with a negative electrode rmade of lossy material land with means for maintaining the Whole of the negative electrode at the t same `continuous potential with respect to the delay line,

in spite of the current due to the impact of the beam electrons on this electrode.

'I'he invention will be better understood from the ensuing description, taken in connection with the appended drawing, wherein:

Fig. 1 represents a transverse section of a cylindrically shaped amplifier4 according to the invention;

Fig. 2 is a radial section along line AA' of Fig. l;

Fig. 3 shows a detail of Fig. l, on a larger scale.

In the tube shown by way of example in Fig. 1, a negative electrode 1 and a delay line 3, parallel to each other, and having a circular structure, are located in a cylindrical envelope 4, closed at its ends by flanges 15 (Fig. 2). 'I'he delay line is coupled to an input 5 and an output 6. A cathode 7 is located opposite a focusing electrode 8, which is insulated from the envelope 4 by supports 16. Cathode 7 is adjacent input 5 and is positioned for shooting an electron beam into the interactionspace bounded by electrodes 1 and 3. This beam is collected at the end of its path by `a collector 9, adjacent output 6. The collector 9 may be integral with a screen 10 which uncouples input and output 6. Feeding connections 11 are provided for bringing cathode 7 to a negative potential with respect to envelope 4, delay line 3 and collector 9, for bringing electrode 1 to a negative potential with respect to delay line 3 and for bringing plate 8 to a suitable positive potential with respect to the cathode 7. Polar pieces 12, shown in Fig. 2, supply an axial magnetic iield, which in fact is transverse to the direction of electron ow. All above mentioned elements are entirely conventional.

According to the invention, electrode 1 is built of a lossy material and is inserted into a peripheral groove United States Patent O ice 2,942,140 Patented June 21, 1960 2 'provid'ed `in the `circularly Vshaped Vmetal support 2, carr`ied Lby a disc 13 secured Ien insulating cross;pie'ees 514, 'asmay be 'seenin iFigs. l and 2. The lossy electrode 1 presents asmo'oth continuous elongatedstripalike sufa'ce substantially the width of the negative electrode structure `and Vhaving its major dimension `generallyin the direction of the `electron beam. Thus, not only is theeurrent which may be caused to ilow in the sole 1, under the `impact of electrons, zreducedto a small intensity because "ofthe high resistivity of the Vmaterial of this electrode 1,

but also the Whole of the sole -1 is kept at a constant "electrical potential by the `highly conductive fs'uppot Z.

Of course any other connections may be `used Vto "the same effect.

iThe thickness of the negative electrode 1 is of the `order of one Aor several times the penetration depth -of the ultra high l:frequency current into the material of which `it is built.

This penetration depth d is given by the well known formula cease,

where `dis expressed in millimeters, the resistivity ofthe material p in en em., the 'wavelength A in the free `space `of the wave propagating in the line in meters and where p is in ohm-cms. and e in c.g.s. units. This condition corresponds to a loss angle of 45.

For instance, for the .1 m. wave length, which corresponds to and. for e=1, p=50 ohm-c-ms.

It is obvious that the above formula is given only by way of example, and that the value of vp may be varied within very wide limits.

Of course the tube described has been given by way of example only. The invention may be obviously applied to any traveling wave tube with crossed electric and magnetic fields, i.e. direct or backward travelling wave amplifiers or oscillators, of circular or linear type.

What I claim is:

l. A travelling wave tube, of the type in which an electron beam is used and which includes means for providing crossed electric and magnetic fields in the interaction space for the electron beam, comprising a. delay line and an electrode parallel to said delay line and bounding therewith said space, having an elongated continuous strip-like surface of lossy resistive material with its major dimension generally in the direction of the electron beam, said surface extending substantially the width of said electrode, said material serving to reduce the noise within said tube normally produced therein by primary stray electrons of said electron beam whenv reaching said electrode during operation of the tube, said electrode including electrically conducting means trode.

-otsetting the effect of said resistive material for keeping the electric potential thereof constant all along this electrode. v s c 2. A travelling wave tube comprising a smooth stripylike electrode made of a lossy material having at the operating wave frequency a loss angle of the order of 45, a delay line parallel to said electrode and bounding ing aconsta'nt electrostaticpotential all along said elec- 3.''A travelling .wave tube comprisingsa smooth strip- Klike Yelectrode made of ia lossy material having at the operating Wave frequency a loss angle of the order of 45, a delay line parallel to said electrode and boundingi therewith an electron and wave interaction space, lmeans '.for producing in said interaction space transverse crossed electrostatic and magnetic elds, means for producing VVan electron beam propagating in said interaction space Ylike electrode made of a lossy material having at the operating wave frequency a loss angle of the order of 459, a delay line parallel to said electrode and bounding therewith an electron and wave interaction space, means for producing in said interaction space transverse crossed electrostatic and magnetic fields, means for producing an electron beam propagating in said interaction space perpendicular to said crossed elds and a conductive Ysupport having a groove, said electrode being located in said groove and having a thickness of the order ofskin depth at said operating frequency, said conductive support being brought to a constant negative potential with respect to said delay line.

5. A travelling wave tube according to claim 1, wherein said electrode has a longitudinal configuration of a circular are and said last-mentioned electrically conducting means includes support means made of highly conductive material to support` the portion of said electrode made of lossy material, said highly conductive material extending substantially `throughout the circular arc defined Iby said strip-like surface of said electrode.

6. A traveling wave tube of the type comprising an anode shaped as a delay line, a smooth strip-likeelectrode made of lossy material and bounding with said delay line an electron and wave interaction space, means for producing in said interaction space transverse electrostatic and magnetic ields in essentially perpendicular relationship to one-another, and means Ifor producing an electron beam propagating through said interaction space essentially perpendicularlyto said lields, said tube including means for maintaining substantially the entire surface of said lossy electrode at a constantl negative potential with 'respect to said delay line, and said delay line being parallel to said lossy smooth electrode.

7. A tube in accordance with claim 6, including a conductivesupport in Contact with substantially the whole f face of said smooth electrode remote `from said interaction space, and means for maintaining said conductive `support at a constant negative potential with respect to said delayline.

f8. A tube in accordance with claim 7,/ wherein said lossy L Velectrode has a loss angle ofthe order of 45 at the operating Wave frequency.

VReferences Cited in the le of this patent UNITED STATES PATENTS s Lerbs A June 17, 1952 2,652,513 VHollenberg Sept. 1 5, 19,53 2 ,680,825 VWarnecke June 8, 1954 2,742,588 Hollenberg Apr. 17, 1956 2,834,915 Dench May 13, 1958 FOREIGN PATENTS V41,067,300 France Jan. 27, 1954 1,081,937 France `lune 16, 1954 705,783 Great Britain Mar. 17, 1954 1,100,854 France Apr. 13, 1955 re r' 

